1. Field of the Invention
This invention relates to rotary power transfer devices and more particularly to providing improvements related to increased transfer efficiency with reduced operating temperature and greater utilization of external interface connections.
2. Description of the Prior Art
One means of transferring electrical power across a rotating interface, even in a vacuum, is provided by the roll ring, a concept described in U.S. Pat. No. 4,098,546, issued July 4, 1978 to Schwartz et al and U.S. Pat. No. 4,372,633 issued Feb. 8, 1983 to Allen et al. Both foregoing patents are assigned to the assignee of the present invention. U.S. Pat. No. 4,098,546 describes the basic roll ring concept of conducting electrical signals and power across the rotating interface by means of a flexible hoop (flexure) captured in shallow grooves in two circular rings. U.S. Pat. No. 4,372,633 describes a roll ring configuration which utilizes a set of multiple flexures between the two rings, a set of idlers to separate the flexures and a set of guides to pilot the idlers, thereby providing multiple paths through the assembly and an increase in current carrying capacity.
There is no known alternate means of transferring large currents at high voltage levels across a rotary interface with the transfer efficiency provided by the roll ring configuration of U.S. Pat. No. 4,372,633. The roll ring configuration, however, presents design and application problems relating to heat transfer, terminal-to-terminal electrical resistance and connection to external power cables.
The present invention addresses the problem of reducing terminal-to-terminal resistance and improving heat transfer from the interior to the exterior of the roll ring module. Materials of high dielectric strength needed to electrically insulate high current and voltage carrying components are also generally poor heat conductors. If the terminal-to-terminal resistance can be reduced, the transfer efficiency is increased resulting in less power being converted into heat. Every interconnection represents a resistance in the series chain between the external terminations in a given circuit. Part-to-part manufacturing tolerances also contribute to this variation of resistance. The external terminations themselves add to the total resistance and also introduce a variableness to the total resistance which may vary each time a connection is made.
Additionally, the power cables used to make connections to the various terminals for various applications are stiff and not only introduce variations in connection resistance, but require adequate working space for the connections. Terminals which face in a given axial direction for one application are not necessarily optimum for other applications.